Within development of medical devices it is of primary focus to develop devices that are safe. Yet it is also of particular concern that the medical devices are as simple and user-friendly as possible. Within medical injectors, such as auto-injectors, it is an aim that it involves no or little needle handling. Before use the needle must be kept sterile.
In some injection devices, the needle is protected by a needle cover, for example a resilient pierceable needle cover, which maintains a sterile barrier around the needle itself. Such needle cover is often assembled together with the needle to form a needle assembly.
By using a flexible pierceable needle cover as sterility barrier the needle can penetrate the sterility barrier thereby obviating the need for removing the needle cover prior to commencing the actual injection procedure. This eases the needle handling significantly. One example of an injector utilizing a pierceable front needle cover is disclosed in U.S. Pat. No. 5,658,259.
For medical injectors that utilize septum-based cartridges to expel one or more doses of a medicament the fluid pathway must be established by docking the injection needle relative to the cartridge. Still, this adds requirements to the sterile barrier system as it must be a safe and simple task to establish fluid communication. WO 2012/022810 discloses a medicament injector which incorporates a pair of flexible pierceable needle covers that prior to use maintains a front needle and a rear needle in a sterile state.
However, design and manufacture of needle assemblies that incorporate flexible pierceable needle covers often reveal issues of varying complexity. For example, if steam sterilization is used, pressure cycles used during the sterilization process may cause the injection needle to penetrate the needle cover thus compromising sterility of the final product. Further, requirements for enabling an effective and short sterilization within short product cycles often require use of needle covers of reduced wall thickness. However, reducing the wall thickness of needle covers will easily lead to further issues or disadvantages.
Further, a number of other factors have to be taken into account in designing needle covers that both provides for fault free operation and superior performance. For example, when utilizing thin injection needles in an injection device, as the device is actuated, the collapse and buckling of the needle cover may lead to non-axial and tilting collapsing of the needle cover which further may result in off-axis contact between the injection needle and the needle cover. Potentially, the injection needle may become bent which ultimately may cause a faulty device. Other important factors include considerations that relate to the force required for collapsing the needle cover as the device is operated such as during needle penetration or during device actuation. One aim is to obtain a low force for collapsing the needle cover.
Having regard to the above-identified prior art devices, it is an object of the present invention to provide a needle assembly and an injection device comprising a needle assembly that are improved with regards to safety in operation.
Yet additional further objects of the invention are to provide measures for obtaining needle assemblies and injection devices having a superior performance and, at the same time, enabling manufacture at a reduced cost.